1. Field of the Invention
The present invention relates to a column base fitting joining a lower end of a column member of a construction structure on the column base fitting and screwed with a top end of an anchor bolt protruding upward from inside a base concrete, and a column base structure using it.
2. Description of the Conventional Art
FIGS. 20 to 22 are reference views explanting a conventional column base fitting 6 and a conventional column base structure 2 using it.
As illustrated in FIG. 20, the conventional column base structure 2 includes a column base fitting 6 including a bottom plate 6c and a support base 6f. The support base 6f is inside a periphery part of the upper surface 6d of the bottom plate 6c and highly protruding upward. A lower end surface of a steel column 4 (column member) is jointed on an upper surface of the support base 6f of the column base fitting 6 by welding. The column base fitting 6 is provided on a base concrete 3 through a mortar 8.
An top end of an anchor bolt 10 penetrating the mortar 8 and protruding upward from inside the base concrete 3, is inserted in bolt insertion holes 6a and 6b in the column base fitting 6 (refer to FIG. 21), and female screws of two nut members 12 (double nuts, refer to FIG. 20), which are stacked up and down, are screwed with a male screw formed on the anchor bolt 10. In such a way, the steel column 4 is stood and fixed on the base concrete 3 through the column base fitting 6 (for example, refer to Japanese Patent Application Laid-Open No. 2003-336266).
The column base fitting 6 in the conventional column base structure 2 is made of a metal and formed to be an approximately plate shape having a square plane and thickness. Further, in the column base fitting 6, bolt insertion holes 6a and 6b penetrating in the thickness direction of the bottom plate 6c (the perpendicular direction to the drawing paper in the figure) are formed in total 12. The outer diameter of these holes is approximately the same and one anchor bolt is loosely inserted in each hole.
One bolt insertion hole 6a in the column base fitting 6 is formed in each four corner portions of the square shape of the bottom plate 6c respectively.
Further, the center position of the bolt insertion hole 6b is located at a position closer to the center of a side in length than the bolt insertion hole 6a in the corner portion, in both ends of the four sides of the square shape.
FIGS. 23 to 26 are reference views explaining a conventional column base fitting 26 and a conventional column base structure 20 using it.
As illustrated in FIG. 23, the conventional column base structure 20 is different from the conventional column base structure 2 concerning having the column base fitting 20 instead of the column base fitting 6. The other constitutions are the same as the conventional column base structure 2.
Namely, in the column base structure 2, the center position of the bolt insertion hole 6a is located at a position slightly shifted closer to the center of the support base 6f from the cross point of two lines. One line passes two center positions of the bolt insertion holes 6b formed at two positions in the length direction of one side in the bottom plate 6c. Another line passes two center positions of the bolt insertion holes 6b formed at two positions in the length direction of adjacent side in the perpendicular direction to the one side.
On the other hand, in the column base structure 20, the center position of the bolt insertion hole 26a is located at the cross point position.
For transmitting the force generated in the steel column 4 by an earthquake, etc., to the base concrete 3 through the bottom plates 6c and 26c, and the anchor bolt 10, the thicknesses of the bottom plates 6c and 26c are designed to withstand a predetermined bending stress. At this time, the thicknesses of the bottom plate 6c and 26c are determined as a value proportional to the tensile strength of each anchor bolt 10 and a distance from the center of the anchor bolt 10 to the lower end position in height of the side surface of the support base 6f and 26f. 